Two-way cable tv conversion system

ABSTRACT

A bidirectional cable television system provides for transmission of signals from cable subscribers downlink in the same direction as the ensemble of television channels which the cable television system is already constructed to deliver. The subscriber signals may be transmitted over the cable in the blanking intervals of a cable television channel, using the T-NET technique described in U.S. Pat. No. 4,750,036. Alternatively, the signals may be carried over a dedicated channel, or transmitted cochannel along a cable television channel carrying ordinary programming by adding the subscriber information to alternating video frames in alternating polarity to achieve visual cancellation. The subscriber signals are collected after the last distribution line amplifier in the cable downlink. The collected signals are transmitted to a central receiver via wireless or other customary means such as a modem. The collected signals may alternatively be transmitted over the air to the central receiver in the blanking intervals of a broadcast television channel using the T-NET technique.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/941,187, filed Sep. 4, 1992, which is a divisional of applicationSer. No. 07/202,206, filed Jun. 3, 1988, now U.S. Pat. No. 5,177,604,which is a divisional of application Ser. No. 07/863,101, filed May 14,1986 now U.S. Pat. No. 4,750,036.

BACKGROUND OF THE INVENTION

This invention relates to improvements to the Interactive Television andData Transmission System technology which this inventor calls T-NET andwhich is described in detail in his U.S. Pat. No. 4,750,036 dated Jun.7, 1988 and divisional Pat. No. 5,177,604 dated Jan. 5, 1993. T-NETprovides bi-directional communication (either wireless or cable) fromone or several central locations to a plurality of fixed or mobilesubscriber transceivers throughout a metropolitan area for applicationsin interactive TV, 2-way data or voice transmission, and the like.Today, such systems are often referred to as interactive TV ormultimedia delivery systems. Furthermore, many CATV (Cable TV) operatorsare desirous of adding telephone and portable (cordless) phone messagedelivery capability to their CATV systems.

Generally speaking, the related T-NET technology disclosed in theinventor's previous patents concern TV signal-compatible modulationmethods wherein data signals to be transmitted downlink to subscribersor uplink from them are placed either: (a) in blanking intervals of aco-channel or adjacent channel "host" television signal oralternatively, (b) the effective polarity of the information is reversedon sequential host TV signal frames and superimposed upon it so as tothereby become invisible to its viewers even though transmittingco-channel. The inventor calls method (b) "data-over-video".

Other related technology disclosed in aforesaid patents concernpartitioning a metropolitan T-NET wireless service area into angularsectors and range intervals in a manner the inventor calls "virtualcellular" so as to gain the advantage of frequency re-use innon-adjacent cells to achieve substantially improved spectrumefficiency. This is made possible because T-NET measures and employs theRF signal propagation time to establish a radio "fence" (using "rangegates") surrounding each transmitting device and thereby eliminates RFcross-talk between devices. This is in effect a combination oftime-division and space division multiplex (TDM/SDM). A related methodthe inventor calls "cellular cable" is taught in the instantapplication.

Yet another related T-NET method disclosed in prior applications is"synergistic modulation" wherein data signals to be communicated toremote locations are superimposed upon another existing but unrelatedlocal (host) signal transmission in such a manner so as tosynergistically employ the carder and some of the spectral or temporalmodulation of the unrelated signal. In this method the remote T-NETreceivers are designed to detect both the data and unrelated host signaland subsequently processes the received data signal as if it were asubcarder of the unrelated host carder signal. This significantlyimproves the transmission reliability and detectability of the data inthe presence of the usually more powerful unrelated signal, whileminimizing or eliminating any interference the data might otherwisecause the unrelated signal, even when aforesaid data and hosttransmissions occur co-channel, or are on adjacent channels, or when thedata and unrelated host signals propagate in opposite directions.

The application of the improved technology taught herein to interactivetelevision and multimedia is of great interest today in the UnitedStates and elsewhere in the world. Improved use of the presentlyassigned radio frequency spectrum without displacing existing users, andmore efficient and expanded use of existing telecommunication facilitiesare principal objects of this invention. Additional detailed backgroundrelating to the instant invention may be found in the patents citedabove.

BRIEF SUMMARY OF THE INVENTION 2-Way CATV

The present invention provides further improvements to the T-NETtechnology. More specifically, one object of these improved T-NETmethods is to provide technology which adds 2-way communicationcapability to existing cable television (CATV) systems, either coaxialcable or fiber optic, with only minor modification of the existing CATVdistribution plant. While T-NET downlink TV signal and data delivery toCATV subscribers follows the customary path, the T-NET uplink deliveryis novel because T-NET does not transmit subscriber responses in theindustry proposed "uplink" direction, but rather in the opposite"downlink" direction propagating along the same path with the ensembleof television channels which the CATV system is already constructed todeliver. Viewer response signals are then extracted from the CATV cablesection anywhere beyond the last distribution line amplifier and theseresponses are forwarded to a central processing facility via wireless orby other customary transmission means. T-NET eliminates the need forretrofitting existing CATV systems with reverse amplifiers.

The inventor rotors to this T-NET application ms "Cellular CATV",because each CATV distribution line is functionally a cell which isalmost perfectly isolated (by line amplifiers) from other cells,consequently each viewer's RF response channel may be re-used inadjacent "cells" with no mutual interference. This cellular spaceisolation, when combined with viewer responses that are also restrictedto specified time slots (in one T-NET embodiment), essentiallyeliminates viewer cross-talk between "Cells" and subscriber cumulativenoise injection problems inherent in today's 2-way CATV systemconstruction proposals which include "reverse amplifiers".

Another object of the instant T-NET improvements is to provide aneconomic and simple retrofit to existing CATV systems wherein theviewer's IR (infra-red) remote control signals are detected in a T-NET2-way CATV retrofit module that is inserted between the CATV subscriberCable end connector and the existing TV set-top converter. This modulerelays the viewer's remote control signals through the CATV cabledistribution lines by the method taught herein, and thence to a centrallocation.

Alternatively, a special purpose RF remote control employing the T-NETcircuits herein described may be used by subscribers to send signals toa passive or active repeater module (herein called an "RF uRelay")inserted between the cable connector and set-top converter as describedabove, but in this method the uRelay module's antenna picks up the RFremote control's RF signal and injects it into the cable of the CATVsystem, thence on toward the central receiving station in the mannerdescribed above. The RF uRelay module may be active or passive. In thisalternative implementation, the inventor's preferred design employs adedicated downlink CATV cable channel to carry subscribers responses andthe preferred modulation is CDMA (code division multiple access) so thatsynchronization of subscribers signals on the CATV response channel isunnecessary. This embodiment is also compatible with future digital (NonNTSC) technology, which is not expected to have blanking intervals.

A variation of this T-NET RF uRelay embodiment would employ RF "cordlessphones" for voice communications and 2-way uRelays could be installed inthe home as well as on streets outside homes to access the CATV cable toprovide city-wide coverage (refer to FIG. 9).

Synergistic Modulation

Another area of T-NET improvements taught in this specification relatesto alternative methods for superimposing non-interfering T-NETdata-over-video signals either at video baseband or at an RF carrier ora subcarrier level. Furthermore, the signal "injection" may be a directwire connection for CATV systems, or over-the-air "mixing" for broadcastsystems. In all these cases the superimposed data is made compatiblewith the television signal upon which it is superimposed to make itinvisible to its viewers.

One embodiment of this improved synergistic method transmits a datasignal "into the air" at a location downstream from an unrelated butco-channel host TV broadcast transmitter; subsequently a T-NET receiverof that data located either upstream or further downstreamsynergistically detects the data and host TV signal. The result is thatthe desired data is communicated more reliably because of the presenceof the unrelated TV host signal which appears to "carry" it as asideband while sharing the same channel, yet the data signal does notcause any perceptible interference to the host TV signal. This T-NETmethod permits TV broadcasters (wireless or cable) to use their existingover-the-air or cable TV channels to send TV signals as well as data toviewers and also to receive their replies, all co-channel, using theirpresent facilities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the application of T-NET technology to adapt anexisting cable TV system for 2-Way interactive TV operation.

FIG. 2 is a detailed block diagram of the T-NET response module (TRM)shown in FIG. 1.

FIG. 3 provides a detailed block diagram of the RTU-MUX illustrated inFIG. 1.

FIG. 4 illustrates how a T-NET retrofit module may be installed in asubscriber's home.

FIG. 5 provides a simplified block diagram of the CATV 2-Way retrofitmodule.

FIG. 6 is a detailed block diagram of the CATV 2-Way retrolit moduleillustrated in FIG. 5.

FIG. 7 is an overall block diagram of a data-over-video response module.

FIGS. 8A-8D present block diagrams of various configurations of theT-NET RF uRelay (microrelay) module and companion RF remote control.

FIG. 9 illustrates an application of the T-NET to adapt existing CATVsystems to provide a multimedia cell (e.g., for a cordless phoneapplication).

FIGS. 10A and 10B illustrate the modulation and spectrum allocation usedby present day NTSC television systems.

FIG. 11 illustrates how the color subcarrier of NTSC is programmed.

FIG. 12A is a time waveform illustration of the standard NTSC signal.FIG. 12B is an illustration of how the T-NET data-over-video issuperimposed.

FIG. 13 is a graphic illustration of the power spectrum of an NTSCtelevision video signal.

FIG. 14A is a spectral illustration of one T-NET data-over-videomodulation method (Option A). FIG. 14B is a detailed illustration ofFIG. 14A.

FIG. 15 is a spectral illustration of two alternative data-over-videomodulation methods (Options B & C).

FIG. 16 is a table illustrating the distribution of power associatedwith each of the NTSC wavetom components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 2-Way CATV

This section describes several unique embodiments of the T-NETtechnology to upgrade existing 1-way cable TV systems for 2-way signaltransmission to and from viewers. The T-NET 2-Way CATV approach is anovel departure from present day 2-way cable TV construction plansbecause T-NET does not transmit viewer responses "uplink" as customarilyproposed; it transmits them downlink. In this specification "downlink"means flow in the direction from CATV head-end toward subscribers.Uplink is the reverse direction.

Reverse cable amplifiers are not necessary in T-NET designs, nor isthere a need for their related bandpass filters and hybriduplink/downlink isolation networks. Basically the existing CATVdistribution system remains 1-way. The T-NET CATV system sends viewerresponses downlink and preferably collects them anywhere alter theoutput of the last cable distribution line amplifier, i.e., at the endof each feeder line. (Generally the responses can be collected at anyamplifier in the downlink and not just the last amplifier.) A principalobject of this invention is to eliminate the very significant cost andproblem of adding CATV reverse amplifiers and collecting, switching, andsorting all (cumulative) viewer responses on the CATV network, togetherwith their cumulative "noise" contribution and sending them "uplink" tothe head-end. It will become apparent from the following discussion thatthis T-NET invention can integrate into future digital TV and"multi-channel" compressed video cable systems as well.

FIG. 1 illustrates a typical CATV network wherein head-end 1 delivers TVprograms to TV receivers 15 via CATV converter 13. T-NET response module21 is integrated with circuits of the CATV converter 13 to enableviewer's responses to travel via cable 7 to RTU-MUX 17, thence by radio(or other means) to central station 20. Specifically, head-end system 1distributes television programs through broadband coaxial or fibre-optictrunk lines 3 to main stations 5 where they are amplified and branchedout through a multiplicity of separate distribution coaxial feedercables 7; each feeder 7 and related assemblies is herein called a "CATVcell" 8. An optional T-NET "cell" program source 6 may be connected tolines 7 to inject special ITV or video-on-demand programming downstreamof head-end 1 for viewing by TV receivers 15 which lie only within cell8. Programming for source 6 may be sent from station 20 by wirelesschannels via antenna 4, or by other means, such as a separatefibre-optic trunk cable 3 directly from head-end 1.

The length of feeder cables 7 in each cell 8 may be anywhere from a fewtenths of a mile to several miles long and may include line amplifiers 9at intermediate points so as to maintain the signal amplitude of all TVchannels within a prescribed system operating level. These amplifiers 9include equalizing networks to compensate for the fact that TV channelsat the high end of the spectrum may be attenuated as much as six timesthe attenuation of low frequency channels. The attenuation in cable 7between amplifiers depends on its length and is typically held to under30 dB. Taps 11 (couplers) are installed along the distribution cable 7near each home to pull-off the television signals and feed them to theTV set-top converter 13 inside each home. These taps include selectablesignal attenuator 12, where the amount of attenuation installed isinversely related to the subscriber distance from the last lineamplifier 9. The taps 11 also include a directional coupler, discussedin a subsequent paragraph. This tap attenuation typically ranges from 5dB to 25 dB. The desired TV signal level delivered to each TV receiveris held uniform and typically is in the range of -40 dBm.

The T-NET/CATV response module (TRM) 21 can be built into 2-wayconverter 13 during manufacture. The response module 21 is relativelysimple as illustrated in detail in FIG. 2. Output RF (radio frequency)transmitter 23 injects viewer's response signals into CATV cable 7 inspecified time slots and is very low in RF power. This injected RFcarrier signal passes through an adjustable attenuator 25. The amount ofattenuation is selected at time of installation and is inversely relatedto the attenuation of the line coupling attenuator 12 for eachsubscriber as discussed above, through which it must pass in reverse.This results in a relatively uniform T-NET signal injection level forall response transmissions traveling along cable distribution line 7.All these T-NET RF response signals travel "downlink" and their carderfrequency lies within one or several channels of the ensemble of TVprograms, preferably in their VBI or HBI. The responses may be eithersuperimposed co-channel with a TV program, or on a dedicated channel ortime slot as may be required in future digital CATV delivery systems.For example, the T-NET RF repeater alternative (FIG. 8) described laterpreferably uses its own dedicated downlink cable channel and uses CDMA(code division multiple access) modulation.

In the case of fiber optic CATV systems, referring to FIG. 2, anequivalent electro-optic transducer assembly would be substituted fortransmitter 23, attenuator 25 and diplexer 27.

Note in FIG. 1 the important advantage offered by this technologybecause each CATV distribution cable effectively forms a unique "CATVcell" 8. Because in most systems today the CATV cable operates 1-way, itis isolated from other cable "CATV cells" by 1-way amplifiers, thuspermitting re-use of response channels in each cell in a manneranalogous to cellular radio telephone. For this reason the inventorcalls this "cellular cable".

Note a further interesting and important point relating to the 2-WayCATV system shown in FIG. 1. According to the present invention, aninjected T-NET response signal can couple from one branch ofdistribution line 7 into another branch when both of these feeder linesare coupled through a line splitter 10. Specifically, referring to thetop center area of FIG. 1, assume an RTU-MUX is placed at the end ofdistribution line #1. In such a case if a T-NET signal is injected intoline coupling tap 11B it will propagate to the left much easier than itwill propagate to the fight because that is the natural path thattelevision signals are designed to travel. This is because coupling tap11B usually incorporate a "directional coupler" which permits signals totravel from left to right along line 7 (FIG. 1) and into each subscriberhome, but inhibit the signals traveling from the subscriber's home andinto distribution line 7 in a direction to the fight.

Consequently T-NET signals injected into coupling device 11B travelrather easily to the left, but then encounter line splitter 10 wherethey are inhibited (attenuated) from jumping across to the otherco-axial line 7 and thence to the RTU-MUX. For example, the line-to-linecoupling attenuation due to line splitter 10 which a signal alongdistribution # encounters in propagating into distribution line #1 couldbe on the order of 35 dB. Nevertheless, this 35 dB attenuation does notdeteriorate the signals transmission from line #2 through splitter 10and into line #1 and on to the end of distribution line 1, thence on tothe RTU-MUX where they are collected. In fact the amount of attenuationa T-NET signal encounters going from line #2 through line splitter 10and into line #1 is not substantially greater than the directionalcoupler attenuation T-NET signals encounter when directly injected intocoupling device 11A for travel kn the right hand direction alongdistribution line #1 to the RTU-MUX. As a consequence of this, only oneRTU-MUX is necessary to collect the signals from both distribution line#1 and distribution line #2. Another way of saying this is thatdistribution line #1 and distribution line #2 together comprise one"CATV cell"

Most cable systems installed today are designed for isolation of futureuplink signals (i.e., viewer responses) from the downlink TV programs inthe frequency domain through use of RF filters at amplifiers 5 and 9.For example, all cable frequencies below approximately 50 MHz areplanned to be used in the future for viewer uplink responses, while allfrequencies above 50 MHz are used today for downlink TV programtransmissions. As noted above, it is technically difficult to aggregateand transmit thousands of uplink subscriber response signals becauseeach viewer also injects a finite amount of noise into cable 7 and thisaccumulates, and because RF broadband noise leakage into cable 7 actslike pick-up from many miniature antennas and can accumulate aconsiderable amount of broadband exterior radio interference (RFI) noiseunless extraordinary care is taken. Coordination of thousands of uplinksignals is also very complex.

The T-NET technology avoids aforesaid problems by not sending viewerresponse signals uplink on the cable to begin with, and by specifyingindividual very low duty cycle time slots within TV blanking intervals(HBI and VBI) in which each subscriber may transmit signals as taught inthe inventor's U.S. Pat. No. 4,750,036. What little noise is injectedinto the CATV cable by each viewer is non-overlapping in time and isconstrained to H or V blanking intervals only, thus it is neveraccumulated or seen on TV screens. Furthermore, only data signalspreceding down a specific CATV cell 8 are collected at the output linesection of the last cable amplifier. Typically only a few dozen to a fewhundred subscribers will employ any one coax feeder line cell 8. Thismakes more bandwidth available per subscriber, minimizes cumulativenoise, and simplifies subscriber transmission coordination (trafficmanagement) problems.

While the T-NET system could transmit in the low cable frequencies setaside in today's CATV systems for future uplink response channels, itwas noted above that those low frequencies would require installation ofspecial filters and reverse amplifiers and hybrid isolation networks toseparate the uplink signals from the downlink signals in the frequencydomain. Since most cable systems do not presently have these componentsinstalled, this is not a practical or economic approach compared to thesimple T-NET alternative taught here. On the other hand all cablesystems today have the proper filters and amplifiers to transmit TVprograms downlink to viewers. The T-NET embodiment of FIG. 1 transmitswithin any one, or several, of the cable TV channels carrying TVprograms, but in their blanking intervals, consequently sharing existingTV channels.

Yet another T-NET viewer response alternative describcd later in thisspecification transmits during the video portion of the TV signal ratherthan in blanking intervals, but using the non-interfering T-NETdam-over-video method. Obviously the T-NET system could also employ avacant downlink TV channel.

Referring again to the viewer response module 21 (FIG. 2) which isintegrated into converter 13, it is typically a very low power RF deviceand includes a digital buffer storage 31, TDM slot selector 29, RFoscillator/transmitter 23, attenuator 25 and diplcxer isolator 27.Alternatively, an electro-optical coupler assembly may be substitutedfor those last three components for application in fiber optic CATVsystems. Required input to the module from existing converter 13circuits include the viewer response digital message to be communicatedand horizontal and vertical (H&V) sync signals for the TV channel withinwhich viewer responses are superimposed.

For existing CATV systems the simplest and lowest cost T-NET approach isto transmit viewer responses in the H and/or V blanking intervals of thesame cable channel assigned to deliver interactive TV (called ITV)programming to the viewer. However, if that ITV channel blankinginterval time is already allocated for other ITV purposes such asdownlink VBI data transmission to viewers, then T-NET couldalternatively transmit responses in the HBI, or by sharing some otherregular TV channel, denoted channel "N", yet still employ the readilyavailable synchronizing signals from the ITV channel being received byconverter 13, providing the ITV program is synchronized at the head-endto that same regular TV channel "N" as described below.

The T-NET response module 21 preferably uses low frequency TV channels,such as TV Channel 2, which is at 54-60 MHz, because it then encountersminimal attenuation traveling down cable 7 and because the T-NETtransmitter circuit can be fabricated very inexpensively at these lowfrequencies. In such a case if the interactive TV channel is, forexample, Channel 50, then at the head end the Channel 50 sync signalgenerator should be synchronized to the Channel 2 transmitter syncsignal so the interactive Channel 50 and Channel 2 are both synchronizedto each other. The converter 13 receiver circuits, though tuned toChannel 50, can then provide the necessary synchronization and referencesignals for a low cost simple T-NET response module 21 which istransmitting ITV responses on Channel 2. Alternatively, response module21 could incorporate its own separate receiver to detect co-channel TVsignals and thereby obtain the sync signals necessary for TRMtransmission in selected TV blanking intervals of any TV channelassigned for communicating co-channel viewer responses. That stand-alonealternative, called a stand-alone retrofit module, is described in thenext section and in FIGS. 8A through 8D.

The T-NET device that collects all viewer responses and attaches to thelast section of each cable distribution line CATV cell 8 is called anRTU-MUX (multiplexed receiver-transmitter). It is illustrated in FIG. 3.For example, if Channel 2 is selected to carry viewer response signals,then the RTU-MUX receiver 33 would be tuned to Channel 2. This receiveris coupled anywhere after the last amplifier in a CATV distribution line7 of each cell 8 using a tap coupler 11 essentially identical to the tapused for coupling TV programs to subscribers. Alternatively, coupler 11frequently is a multiple tap device and any vacant tap could be used forthe RTU-MUX.

An arrangement could be made to install the RTU-MUX 17 (FIG. 1 ) in asubscriber's home or at another location (e.g., a convenience store orgasoline station) so that the RF output of transmitter 41 can betransmitted by antenna 19 to a central location 20 using the local T-NETwireless system described in the inventor's U.S. Pat. No. 4,750,036, oralternatively, a telco modem 43 could be connected to a dedicated phoneline 45 to transmit viewer responses back to the central location.Alternatively, a microwave uplink could be provided.

CATV Retrofit Response Module

At the present time there are about 50 million cable TV subscribers inthe United States serving about 60% of the population and most have a1-way CATV converter box. Consequently it is highly desirable to keepmost of these converter boxes in operation throughout their useful life.A T-NET retrofit response module (TRM) will permit 2-way transmissionsretaining the present CATV converter by simply providing for insertionof the TRM between the cable converter and the co-axial cable outputwhich feeds it, as illustrated in FIG. 4. Normally incoming co-axialcable 14 connects CATV signals to existing cable converter 18, however,for 2-way CATV service a new T-NET stand-alone response module 22 isplaced on top (or nearby) existing converter 18. A new co-axial cable 16connects TRM 22 to converter box 18 to provide both TV and ITV programs.Either an existing "universal" or special IR remote control 20 controlsexisting converter 18 as well as TRM 22 through IR sensors 26 and 24 andperhaps also the TV receiver. FIG. 5 is an overall block diagramillustrating this retrofit module 22 functional configuration.

T-NET response module (TRM) 22 is shown in greater detail in the blockdiagram of FIG. 6. The TV channel the TRM is assigned to operate on ispicked up by coupler 11 and sent to receiver 49 through an isolatorcircuit 47. Receiver 49 detects downlink data, compressed (digital)video and synchronizing signals as well as time codes that enable TDMslot selector 29 to uniquely select a pre-assigned time slot in whichthis particular subscriber is assigned to transmit on. That time slotalso corresponds to the address for that particular TRM and uniquelyidentifies the subscriber. Receiver 49 also detects and outputs downlinkdata to viewers that may be transmitted, for example, in the VBI of thechannel to which receiver 49 is tuned. Receiver 49 can also detectdigital data-over-video to provide an additional (optional) "compressed"TV channel which is superimposed on a regular TV channel in the mannerdescribed later in this specification.

The downlink VBI data is sent to memory 51 for storage. Memory 51 alsostores any programming instructions to operate the microprocessor aswell as other control information. Control of module 22 is providedthrough the viewer's remote control 20 and IR receiver module 24 ascommanded by the subscriber. For example, if the subscriber wishes toreview a television program listing (which is constantly updated throughreceiver 49), then this information is retrieved by microprocessor 53from memory 51 and loaded into graphics generator 55. The graphicsgenerator drives an RF generator/modulator 57 which outputs a compositevideo RF signal and couples it through uni-directional coupler 12 to TVreceiver 15 for display. The subscriber, using the remote control 20,may then, for example, scroll through the TV guide, automaticallyprogram his VCR, or do other things with the information so displayed.

A subscriber, using remote control 20, may transmit responses to TV gameshows, TV surveys, conduct transactions and the like by pressing thekeys of the remote control which then sends an IR beam signal to module24 thence to microprocessor 53. The microprocessor formats this viewerresponse and applies it to AND gate 59. At the appropriate time slot asdetermined by the TDM slot selector 29, a gating signal is applied tothe second terminal of AND gate 59 so that the viewer response messageis then applied to modulator 65 which in turn transmits that message"downlink" on cable 7 via isolator 47 and coupler 11. Oscillator 63 andcrystal 61 generate the RF carrier for that viewer response.

Referring again to FIG. 6, optional circuits 50 and 52 detect anduncompress an optional data-over-video downlink video signal and convertit to NTSC format (or other formats). That NTSC signal is sent to RFgenerator/modulator 57 where it is put on an RF carrier, typically on TVchannel 3, for transmission as NTSC composite video to TV receiver 15for viewing.

FIG. 7 teaches the inventor's data-over-video method of transmittingviewer responses co-channel down the CATV cable as an alternative to theblanking interval (e.g., VBI) data transmission method described above(FIG. 6). In this method the viewer digital response is transmittedduring the video portion on one or several pre-assigned TV horizontalscan lines which also carry regular video pictures to the viewer, but insuch a manner that the digital data is sent in a first polarity on oneTV frame and subsequently it is repeated in the opposite digitalpolarity on the following frame so that the visual effect of the datacancels and becomes essentially invisible to the viewer of theparticular video channel on which this data is superimposed. Toaccomplish this cancellation, the viewer's response digital data ratemust equal an odd harmonic of one-half the standard TV horizontal scanrate, as will be described in a subsequent section of thisspecification. Suffice it to say at this point that the specific pictureelements (pixels) where the data appears "bright" on one TV frame,reverses on a subsequent frame and appear "dark"; thus to the viewer'seye the cumulative data effects cancel.

One way to allocate the dam-over-video viewer response CATV cabletransmission capacity is to assign perhaps one-half of one TV videohorizontal line to a specific subscriber during any given communicationsession to send, for example, a 128-bit word. The second-half couldlikewise be assigned to another viewer. Since there are 483 active videolines (the rest of the 525 lines are in the VBI) in each NTSC TV frame,and two frames are needed to transmit the viewer's data word, this wouldprovide capacity for 926 viewer responses for each selected TV channel,for each coaxial cable distribution line cell 8. Since there are 30 TVframes per second, each of 923 subscribers could consequently transmit1920 bps (net) simultaneously in each cell 8. Obviously more TV channelsare available and could be used to increase this capacity. Otherallocations for each subscriber could be used to provide capacity totransmit digitized voice signals to and from subscribers.

Alternatively, some of the horizontal video lines could be assigned tocarry downlink data to viewers, while other lines could carry uplinkdata from viewers. For example, a cell program source 6 (FIG. 1) couldtransmit compressed dam-over-video TV programs to modules 22 (FIG. 7)where they would be processed by circuits 50 and 52 and sent to TVreceiver 15 for viewing. The technical details of this method aredescribed more fully in a subsequent section. Note that this method isnot restricted for use on present day NTSC type television formats only;in the future T-NET technology could also be used with advanced digitaltelevision methods.

RF uRelay Module

FIGS. 8A through 8D illustrate an RF uRelay (microrelay) module whichaccomplishes a function comparable to the retrofit response moduledescribed in the preceding section. Referring to FIG. 8A, RF uRelaymodule 67 inserts between the end connector of CATV cable 14 and theexisting CATV converter 18, via cable 16, in the manner describedearlier. A radio frequency (RF) remote control 73 operated by the TVviewer transmits radio control signals through its antenna 69 to antenna70 on uRelay module 67.

The RF remote control 73 is shown in greater detail in FIG. 8B. Akeyboard 75 controlled by the viewer generates commands tomicroprocessor 79 which operates in conjunction with memory 77.Microprocessor 79 reformats the commands as necessary and applies themto CDMA (code division multiple access) modulator 83. Modulator 83superimposes these commands on RF oscillator/transmitter 81 where theyare transmitted to the RF uRelay module 67 through antenna 69.

Various forms of modulation could be employed in this RF uRelay designbut the CDMA method is preferred because it minimizes or eliminates theneed for synchronization of viewer response transmissions. It is wellknown by communications engineers that CDMA transmissions may besuperimposed upon each other (within certain well known limits) withoutany mutual interference and these signals can later be sorted out at thereceiving location using the proper demodulation code. CDMA usuallyemploys various forms of spread spectrum modulation.

In the RF uRelay module embodiments shown in FIG. 8A through 8D it ispreferred that a separate exclusive downlink CATV channel be allocatedfor viewer responses. However, it is obvious from the teachingspresented above that the CDMA modulation could alternatively beconstrained to blanking intervals of existing CATV television programsand thus viewer responses could be transmitted co-channel with a TVprogram in a variation of this RF approach. However, future advanceddigital television systems are not expected to employ blanking intervalslike the present day NTSC standard, hence a separate response channel ispreferred for these future systems.

The CDMA mutual interference between simultaneously responding viewersis further minimized by virtue of the fact that each viewer naturallyholds a unique physical position along the CATV coaxial cable.Consequently viewers are spread out in time and distance according totheir position along the coaxial cable and this aids in preventing exactoverlap of viewer responses, hence minimizes CDMA "overload" uponmassive viewer responses as might occur when all ITV viewers are askedto respond to a specific question. It is estimated that at least onethousand viewers could respond essentially simultaneously on any onedistribution line CATV cell 8 using CDMA. A further advantage of thisT-NET CDMA method is that the coaxial cable transmission media is "wellbehaved" (as compared to wide amplitude propagation variations seen inover-the-air radio transmissions) consequently all response signallevels are kept at a uniform level, eliminating dominant CDMA signalsthat could mask out weaker CDMA signals.

The output of the RF remote control 73 is detected by antenna 70 of theRF passive uRelay as shown in FIG. 8C. That signal is sent throughbandpass filter 71 and is connected directly to CATV cable 14 by coupler12. This is a completely passive low cost method for injecting viewerresponses directly into the coaxial cable of the CATV system. Thebandpass filter 71 minimizes infiltration of broadband RF noise intocoaxial cable 14.

Alternatively, FIG. 8D illustrates an active RF uRelay which functionsessentially in the same manner as the passive uRelay described in FIG.8C. Amplifier 73 is inserted at the output of bandpass filter 71 toincrease the power of the response signal before it is injected intocable 14 via coupler 12. In either FIG. 8C or 8D the coupler 12 can be auni-directional device to minimize energy leakage toward the CATVconverter. This directional coupler is not mandatory, however, since theamount of energy injected into CATV cable 14 is very low level and willnot harm CATV converter 18, nor will it interfere with any of the activeTV channel video programs.

FIG. 9 illustrates a "multimedia cell" configuration of the T-NETtechnology wherein an RF (radio frequency) repeater 66 with antenna 70is positioned so as to detect the radio transmissions from a portabletransceiver 72 emitting through its antenna 69 signals such as voicetransmissions for so called microcellular or cordless phoneapplications. The signals injected by 66 into the CATV co-axialtransmission line 7 travel along the same path as the ensemble oftelevision signals in the manner previously described and these signalscan be detected at a terminating RTU-MUX 17 which is coupled to theco-axial line 7 by the coupling device 11 in the manner previouslydescribed. Signals from the RTU-MUX 17 are thence transmitted viaantenna 19 to a central receiving station 20. Signals from centralstation 20 to repeater 66 travel on CATV line 7 with the TV signals aspreviously described.

DATA-OVER-VIDEO

The T-NET data-over-video process involves the following steps:

1. The superposition of a data signal on a host video signal in a firstTV video frame, followed by the superposition of inverse data (data) ina following TV frame. This two-frame data superposition results inapparent video cancellation of the data signal on the TV screen, in sofar as the human eye is concerned.

2. The data superposition referred to above may be injected at theoriginating host signal source, or at a time or location other than theplace and time of origination of the host video signal, and bymodulation means applied on the host video baseband signal, or itscarrier, or on a subcarrier signal.

3. The subsequent detection and demodulation of the data signal atremote receiver locations is carried out with reference to the hostvideo signal and/or its carrier or subcarrier. The inventor refers tosteps 2 and 3 above as synergistic modulation/demodulation (see U.S.Pat. No. 5,177,604 for additional description).

This data-over-video process is analogous to the related modulation andvisual canceling effect of the chroma subcarrier signal whensuperimposed on monochrome video as set forth in the NTSC televisionstandard. However, unlike the case of NTSC chroma modulation, in theT-NET concept the data signal is designed to exactly cancel because itis duplicated and inverted in alternate TV frame pairs. NTSC basebandvideo is not duplicated and inverted frame-to-frame, nevertheless,because the chroma video modulation is derived from and highlycorrelated with the monochrome video scenes, the viewer's eye is more"forgiving" of those artifacts. On the other hand the data signalmodulation herein proposed is independent of, and although correlatedwith sync pulses it is not correlated with the host video; consequentlymore care is required to avoid generating interference and artifacts.

It should be pointed out that from a technical standpoint the inventor'ssynergistic modulation does not require the knowledge or cooperation ofthe originator of the host video signal (for example, the TVbroadcaster). While there may be administrative issues involved inapplying this process (e.g., the FCC's present "must carry" rules), onlythe technical issues are considered here.

To reiterate, the synergistic dam-over-video process taught here may becarried out by superposition of data on host video at (1) baseband levelor (2) subcarrier level or (3) RF level. The baseband and subcarrierinjection process is more easily understood by communication engineers,however, the process of data injection at RF level is very novel and ismore difficult to comprehend.

Review of NTSC

It is instructive to review the NTSC television modulation standard inorder to provide a background for discussing and understanding the T-NETdata-over-video concept. Pertinent aspects of the NTSC color televisionstandard are summarized in FIGS. 10 and 11. The vector diagrams at 10Aare a reminder of the three basic modulation processes applied on the TVmonochrome (picture) carrier, and color subcarrier. The picture carrieremploys a hybrid single sideband (SSB) modulation process because aboveabout 800 KHz it is SSB while below 800 KHz both sidebands are retained(a vestigial lower sideband) and thus in that area it is regular doublesideband (DSB) AM. The invention takes advantage of this fact as pointedout in a later section.

The color subcarrier is a hybrid QAM (quadrature amplitude modulation)process. The inphase (I) component of the color subcarder is intended toprovide a 1.5 MHz bandwidth even though the upper sideband is truncatedabove approximately 500 KHz (FIG. 10B), resulting in sideband asymmetrysimilar to picture carrier modulation described above. On the otherhand, the Q component of the color subcarder retains symmetrically bothits sidebands and has a modulated bandwidth of approximately 500 KHz.The chroma subcarder, shown dotted in FIG. 10A (DSBSC), is suppressed.FIG. 10B shows the NTSC spectrum allocation.

Because the upper sidebands of the "I" component of the modulated chromasubcarder is truncated above approximately 500 KHz, a compensatingfilter process at the TV receiver would normally be required, but foreconomic considerations this is often ignored. In addition, and perhapsin partial compensation for the fact that many receivers do not includeideal processing, the "I" component lower sideband is frequently rolledoff below the 1.5 MHz desired bandwidth.

A vector diagram showing the relation of the various colors conveyed bythe "I" and "Q" channel components is presented at FIG. 11. It issignificant to the following discussion to point out that the NTSCchroma subcarder transmission/reception process in actual practicedelivers a phase angle accuracy (tolerance) on the order of twoelectrical degrees in its definition of color (hue). This implies arelatively good signal-to-noise (S/N) ratio for most TV signals, on theorder of 30 dB or higher for the chroma signal in typical applications.

The top of FIG. 12 illustrates the time domain allocation of the NTSCsignal amplitude range, particularly during the horizontal blankinginterval (HBI). The 100% modulation range (to peak-of-sync) of the TVtransmitting signal is defined by industry practice to equal 160 IREunits.

The useful video amplitude span from white level to black level occupiesa modulation range from 12.5% to 70.3%. In IRE units, this correspondsto a 7.5 IRE to 100 IRE video range. Note that the chroma sync burstswings ±20 IRE and is allowed to penetrate during fly-back into thevisual range, i.e., its negative sine wave peak excursions swing "gray"to the extent of 12.5 IRE. Nevertheless, the chroma sync burst does notbecome visible to the human eye in older TV receivers because its phaseis inverted 180 degrees on alternate TV frames, partially cancelingvisual artifacts it might otherwise cause. This chroma sync burstpenetration into the visual range, and its resulting visualcancellation, is similar in principle to cancellation in the T-NETconcept. Most newer TV receivers provide circuit enhancements that drivethe screen more "blank" in the VBI and HBI, eliminating all chroma burstvisual effects.

Data Signal Injection

The illustration at the bottom of FIG. 12 shows the basic T-NETdam-over-video superposition concept in the time domain. During thestandard 53 uSec video pedestal, data is shown superimposed on a videosignal under three different cases: data Case A is in the mid-range ofthe video amplitude, data Case B is at or near the black level, and dataCase C is at or near the white level. Here data Case A will be primarilydiscussed. The data Case B is interesting because the inventor'scircuits purposely drive the modulation deeper into the black level sothat both data and inverted data stay in the black while in data C casesthe data and video modulation is driven into the white level. The reasonfor this is because for a signal level which is already black butbecomes gray due to superimposed data on one frame, it becomes difficultto make it look blacker than black on a second frame. The converse istrue in the data Case C.

It is pointed out in a later section of this specification that asuperimposed T-NET data modulation amplitude increment/decrement on theorder of 5 or 6 IRE on the video waveform appears feasible and providesadequate signal-to-noise (S/N) margins.

Any alien signal superimposed upon an NTSC video waveform pedestal whichis intended to invert on every other TV frame so as to visually cancelwill, because of this restriction, appear in the frequency domain as aseries of spectral lines which lie between (i.e., interleaved) thespectral lines that comprise the video signal itself. The reason forthis is that any signal riding on the periodic video pedestal (15,734Hz) which is intended to visually cancel by alternating its polaritymust possess a fundamental frequency which is an odd multiple ofone-half the television horizontal scan (H-scan) frequency. The bestillustration of this canceling phenomenon is the choice of frequency forthe NTSC chroma subcarrier; it too is a odd multiple of one-half thehorizontal scan rate, in this case a multiple equal 455.

An NTSC color subcarrier at a multiple of 455 times one-half the H-scanrate results in a frequency of 3.579545 MHz, which is the well knownchroma frequency. In the QAM NTSC modulation process the subcarrier issuppressed (DSBSC) but nevertheless the "I" and "Q" sidebands thatremain still possess the flame-to-frame alternating polarity requiredfor visual cancellation. This is not an exact cancellation for reasonsnoted before.

FIG. 13 illustrates the spectral distribution of a typical wellmodulated video NTSC test slide known as "Tulip Garden" (ref: TelevisionEngineering Handbook, L. B. Benson, McGraw-Hill 1986, FIG. 5-24). Notethat the chroma signal modulation peak level (shown dotted) is typicallymore than 20 dB below the peak-of sync level for the monochrome signalspectrum. FIG. 13 is calibrated in volts per unit bandwidth, thisrepresents 20 dB per horizontal division. Note that the relative powerper unit bandwidth is down nearly 60 dB at the cross-over between themonochrome spectrum and the lower sideband chroma spectrum. In this casethe cross over is at about 2.7 MHz above the TV carrier. L. B. Benson(op cite) also shows the relation between the power spectrum of thechroma signal and the monochrome signal for the case of acolor-bar-chart TV test signal; the cross-over between the chroma andmonochrome spectrums is again on the order of 55 dB to 60 dB below the"DC" carrier term of the monochrome signal (i.e., TV peak-of-sync).

From the discussion so far it can be seen that signal isolation betweenthe TV monochrome and chroma signals results from isolation in thefrequency domain. In the time domain the monochrome and chroma waveformsare superimposed. In the frequency domain the spectral lines of thechroma signal and monochrome signal are isolated from each other and areinterleaved. Note further that in the frequency region where the chromasignal is located the chroma sidebands are from 10 dB to 40 dB above thelevel of the monochrome spectrum which occupy the same spectrum area,yet do not interfere with monochrome (black and white) TV receiversbecause of frame-to-frame phase reversal.

Recall that the monochrome signal is amplitude modulated on thetelevision signal carrier and below about 800 KHz it is double sideband.It is pointed out below that at least one new baseband data signal,denoted an "associated information signal," could therefore be arrangedto be in quadrature with the AM monochrome signal sidebands, henceisolated from it because of its quadrature (e.g., phase modulation, PM)relation, provided the data sidebands are below 800 KHz, i.e., below 800KHz the AM-TV and PM-Data would not "cross-talk".

In other words a quadrature modulated (e.g., PM) data signal could besuperimposed upon a double sideband amplitude modulated (AM) signal withminimal mutual interference and without the need to provide frequencyinterleaved spectral lines. On the other hand, PM data signals aboveabout 800 KHz cannot be so isolated because the TV monochrome AM issingle sideband there (hence it has "residual" PM) and wouldconsequently conflict with the AM signal. Therefore above about 800 KHz,signal isolation must be provided for by interleaving data signalsbetween the spectral lines of the monochrome signal and this indeed iswhat the conventional NTSC subcarrier provides.

What the above discussion is leading to is that for "baseband" datamodulation below about 800 KHz one could rely on a superimposedquadrature modulated (PM) data signal for isolation, but above 800 KHzone must insert alien signals so they lay between the spectral lines ofthe monochrome signal. A combination of both methods is also possible.This inventor employs one such combined approach, as discussed in alater section of this specification.

FIG. 14A illustrates the superposition of a T-NET data signal modulatedon an interleaved new subcarrier having a frequency of 2.006118 MHz, forexample. This is a frequency 255 times one-half the H-scan rate,consequently providing video cancellation on every other frame. This iscalled T-NET option A. The subcarrier for option A could also be placedabove the chroma subcarrier.

If one employs 8-QAM on option A subcarrier for data modulation, witheach of the two 8-QAM orthogonal components operating at a symbol rateof 650 Kspm, yielding 3 bits/symbol, it would provide a net datathrough-put of 1.5 Mbps; a design goal for future compressed full motionvideo and sound. The spectral appearance of this superimposed datastream on the NTSC signal is shown in more detail at FIG. 14B. Thisoption A is an example of T-NET data injection at subcarrier level. Theresult is a composite TV signal with two QAM subcarriers, rather thanthe usual one (i.e., the chroma subcarrier and data subcarrier). Theinventor has found this two subcarder option to be practical if the datasignal injection level is carefully adjusted as discussed in a followingsection.

FIG. 15 illustrates two alternative methods (options B and C) of datasuperposition, but this time at baseband. The baseband signal injectionoption B process was demonstrated by the inventor at RF level bymodulating the data stream (at the required odd harmonic rate) on aseparate T-NET RF carrier, independent of and not co-located with thehost RF carrier source which was modulated by a regular TV signal.Equivalent baseband superposition was accomplished by subsequently "zerobeating" (phase-locking) the T-NET and host TV carders with the resultthat the data sidebands became interleaved between the spectral lines ofthe TV video sidebands in the desired manner described above; i.e., asif the process had occurred at "baseband" at the video source. Oneadvantage of this additive process is that it can be done "downstream"of the TV signal transmitter (e.g., over-the-air or on cable) withoutthe need to coordinate with the host TV broadcaster.

Option C shown in FIG. 15 is illustrated by the vector diagram at thelower fight side of FIG. 15. The intention is as follows: the datastream is divided into two components, "I" and "Q". The modulation is atTV signal baseband. The data "I" term is in-phase with the host video RFcarder, consequently its modulation could conflict with the TV videomonochrome modulation, however, it is arranged so the "I" data on the TVvideo will be inverted on alternate frames as already discussed,therefore eliminating undesired video cross-talk effects. The data "Q"component on the other hand is in quadrature with the TV videomodulation and under 850 KHz, consequently minimal or negligiblecross-talk from the Q data stream will be encountered. The modulationrates used in this process can be on the order of the rates previouslydiscussed in relation to FIG. 14. For example, a data rate of at least650K symbols per second on each of the two quadrature data componentsand 3 bits/symbol could be employed, yielding a through-put of 1.5 Mbpsor greater. Note that in option C symmetrical sidebands above and belowthe video carder can (and must) be provided because the data symbol rateis only 650 Kspm, thus under the TV monochrome AM double sidebands whichextend to about 800 KHz.

The preferred data-over-video modulation options shown in FIGS. 14 and15 may be summarized as follows:

Option A: Add a 2nd data subcarrier below or above NTSC TV host signalchroma subcarrier. Employ 8-QAM (or higher) data modulation for 1.5 Mbpsnet data rate.

Option B: Modulate AM data stream using QAM onto NTSC host TV carrier atdata rate equal odd harmonic of H-sync/2.

Option C: Split data stream into I & Q component and add to NTSC TVbaseband signal (or at equivalent RF level). Q term is PM and I term isAM at bit clock equal to odd harmonic of H-sync/2.

Data Signal Power Level Adjustment

This disclosure shall now address the critical issue of determining theoptimum amplitude of the superimposed data signal relative to the hostTV signal amplitude.

FIG. 16 is a table which estimates the manner in which power isdistributed within an NTSC TV signal with a superimposed data signal.Various waveform components of the NTSC TV signal are shown on differentlines of this table and their waveform (e.g., pulse width) and relatedfundamental range in the frequency domain are shown in the first threecolumns. For example, the video pedestal, which it will be recalled hasa minimum amplitude of 12.5% modulation, a pulse width of 53 uSec and apulse repetition rate of 15,734 Hz. Its fundamental bandwidth is 18.8KHz around each side of the video carrier frequency. An all white videopedestal of 12.5% amplitude would contain 1.8% peak of sync power,whereas an all black level video pedestal would contain 49.4% of thatpower.

If digital data pulses are superimposed on this TV video waveform and,for data signal power estimates, each TV pixel width is assumed equal tothe width of a data pulse, the amount of power in the T-NET video ± datasignal can be determined. This question was already discussed briefly inreference to FIG. 12. At the bottom left of FIG. 12 two data pixels areshown for TV frame N. A corresponding but inverted pair of data pixelswould appear at the same location for TV frame N+1. The peak power ofthese video pixels when it has a digital "1" data pulse superimposed ascompared to when it has a "-1" digital pulse subtracted can beestimated. Note (FIG. 12) that in the data "A" case, the Video plus datapixel with a "1" on it would reach approximately 23% relative RF powerlevel, while a Video minus data pixel with a "-1" digital pulse wouldreach about 17% RF power level. The difference between these two levelsbeing 6%, all relative to peak of sync power.

On the other hand if a similar estimate for the white level of data Case"C" is made, the power increment and decrement caused by data pulseswould be significantly less. On the other hand, Black level data (caseB) yields much higher data power. Consequently, assuming the data signalamplitude is a fixed IRE value (e.g., ±6 IRE), the power associated withthe T-NET data signal depends upon the level of the video upon which itis superimposed. The last three lines in FIG. 16 estimate the relative(re peak-of-sync) power percentage associated with the superimposed datasignal for three video signal levels: white level, mid-level, and blacklevel. These data power estimates range from about 1% to 5% of the TVpeak of sync power. The inventor has found that on average such datapower levels appear 6 to 10 dB below the typical chroma subcarriersignal level when seen on the spectrum analyzer.

The last two columns of FIG. 16 relate these data modulation levels andcorresponding signal power to the estimated data signal-to-noise ratiothat would result at a T-NET data receiver for a worst case TV signalcondition. For terrestrial over-the-air television, this occurs at theTV grade B signal level (lowest commercially usable signal). At theworst case grade B contour a digital data stream modulated at the levelssuggested in FIG. 10 (±6 IRE) would result in an estimated minimum S/Nof 17.6 dB with data superimposed at the white video levels and rise toa S/N of 25.1 dB when superimposed on video at the black level. Thisappears to be acceptable S/N for the preferred 8-QAM modulation becausethis corresponds to equivalent phase noise levels ranging from ±7° to±3°, not unreasonable compared to the 45° increments of 8-QAM, duringworst case conditions. These could be improved in CATV applicationswhere 16-QAM or even 32-QAM could be used for greater data through-put.While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:
 1. In an interactive television system, a method forcommunicating information to at least one central receiver from at leastone remote receiver location, each remote receiver location connected toa cable television system, the cable television system for transmittingat least one video signal in a downlink direction over at least onecable, the at least one cable having at least one amplifier along the atleast one cable, each amplifier serving at least one remote location,the method comprising the steps of:(i) at at least one remote location:(a) modulating the information to be communicated from the at least oneremote location onto a first carrier; (b) transmitting the modulatedfirst carrier of step (i)(a) onto the at least one cable only during atleast some of the blanking intervals of a first cable channel; (ii)after at least one cable amplifier in the downlink direction from the atleast one remote location:(a) detecting the modulated informationreceived on the at least one cable and retransmitting the modulatedinformation over the air on a second carrier during at least some of theblanking intervals of a first broadcast channel.
 2. The method of claim1, wherein the at least one cable amplifier is a last cable amplifier inthe downlink direction.
 3. The method of claim 1, whereinafter the atleast one amplifer, the at least one cable comprises a firstdistribution line and a second distribution line branching from asplitter, and the transmitting step comprises the step of transmittingthe modulated first carrier onto the first distribution line, and thestep of detecting and retransmitting comprises the step of detecting themodulated information on the second distribution line and retransmittingthe modulated information from the second distribution line, wherein thefirst and second distribution lines comprise a cable television cell. 4.The method of claim 1, wherein the at least one amplifier isunidirectional in the downlink direction.
 5. In an interactivetelevision system, a method for communicating information to at leastone central receiver from at least one remote receiver location, eachremote receiver location connected to a cable television system, thecable television system for transmitting at least one video signal in adownlink direction over at least one cable, the at least one cablehaving at least one amplifier along the at least one cable, eachamplifier serving at least one remote location, the method comprisingthe steps of:(i) at at least one remote location:(a) receivinginformation from a wireless remote control device; (b) modulating theinformation go be communicated from the at least one remote locationonto a first carrier; (c) transmitting the modulated first carrier ofstep (i)(b) onto the at least one cable only during at least some of theblanking intervals of a first cable channel; (ii) after at least onecable amplifier in the downlink direction from the at least one remotelocation: (a) detecting the modulated information received on the atleast one cable and retransmitting the modulated information over theair on a second carrier during at least some of the blanking intervalsof a first broadcast channel.
 6. The method of claim 5, wherein theremote control device transmits the information over an infraredcommunications link to the at least one remote location.
 7. The methodof claim 5, wherein the remote control device transmits the informationover a radio frequency link to the at least one remote location.
 8. Themethod of claim 7, further comprising the step of modulating theinformation by a code division multiple access (CDMA) technique beforethe remote control device transmits the information.
 9. In aninteractive television system, a method for communicating information toat least one central receiver from at least one remote receiverlocation, each remote receiver location connected to a cable televisionsystem, the cable television system for transmitting at least one videosignal in a downlink direction over at least one cable, the at least onecable having at least one amplifier along the at least one cable, eachamplifier serving at least one remote location, the method comprisingthe stems of:(i) at at least one remote location:(a) modulating theinformation to be communicated from the at least one remote locationonto a first carrier; (b) transmitting the modulated first carrier ofstep (i) (a) onto the at least one cable only during at least some ofthe blanking intervals of a first cable channel; (ii) after at least onecable amplifier in the downlink direction from the at least one remotelocation:(a) detecting the modulated information received on the atleast one cable and retransmitting the modulated information over theair on a second carrier during at least some of the blanking intervalsof a first broadcast channel; (iii) at at least one central location:(a)receiving the transmissions of step (ii)(a) and detecting theinformation therein.
 10. In an interactive television system, a methodfor communicating information to at least one central receiver from atleast one remote receiver location the remote location comprising arepeater, each remote receiver location connected to a cable televisionsystem, the cable television system for transmitting at least one videosignal in a downlink direction over at least one cable, the at least onecable having at least one amplifier along the at least one cable, eachamplifier serving at least one remote location, the method comprisingthe stems of:(i) at at least one remote location:(a) receivinginformation from a wireless transmitter; (b) modulating the informationto be communicated from the at least one remote location onto a firstcarrier; (c) transmitting the modulated first carrier of step (i)(b)onto the at least one cable only during at least some of the blankingintervals of a first cable channel; (ii) after at least one cableamplifier in the downlink direction from the at least one remotelocation:(a) detecting the modulated information received on the atleast one cable and retransmitting the modulated information over theair on a second carrier during at least some of the blanking intervalsof a first broadcast channel.
 11. The method of claim 10, wherein thewireless transmitter is a cordless telephone.
 12. An interactive cabletelevision system for communicating information from at least one remotelocation along at least one cable, the system comprising:at least oneamplifier along the at least one cable for amplifying signalscommunicated along the at least one cable; a cable head transmitter fortransmitting at least one video signal downlink over the at least onecable; a response module at at least one remote location along the atleast one cable, the response module comprising:a modulator formodulating the information onto a first carrier; a transmitter fortransmitting the modulated information onto the at least one cable onlyduring at least some of the blanking intervals of a first cable channel;and a multiplexed receiver/transmitter, coupled to the at least onecable after at least one amplifier in a downlink direction from theresponse module, for detecting the modulated information and forretransmitting the modulated information to a central receiver.
 13. Thesystem of claim 12, wherein the multiplexed receiver/transmitter iscoupled to the at least one cable after a last amplifier in the downlinkdirection.
 14. The system of claim 12, wherein after the at least oneamplifier,the at least one cable comprises a cable television cellincluding a splitter, and a first distribution line and a seconddistribution line branching from the splitter, the transmitter includescircuitry for transmitting the modulated information onto the firstdistribution line, and the receiver/transmitter includes circuitry fordetecting the modulated information on the second distribution line andfor retransmitting the modulated information from the seconddistribution line.
 15. The system of claim 12, whereinthereceiver/transmitter includes circuitry for retransmitting the modulatedinformation on a second carrier over the air during at least some of theblanking intervals of a first broadcast channel.
 16. The system of claim12, whereinthe receiver/transmitter includes circuitry forretransmitting the modulated information on a second carrier over theair in a dedicated frequency band.
 17. The system of claim 12,whereinthe receiver/transmitter includes circuitry for retransmittingthe modulated information onto a telephone line.
 18. The system of claim12, wherein the at least one amplifier is unidirectional in the downlinkdirection.
 19. The system of claim 12, wherein the module furthercomprises a module receiver for receiving the information, the systemfurther comprising a remote transmitter for transmitting a wirelesssignal conveying the information to the module receiver.
 20. The systemof claim 19, wherein the remote transmitter transmits the information tothe module receiver over an infrared communications link.
 21. The systemof claim 19, wherein the remote transmitter transmits the information tothe module receiver over a radio frequency communications link.
 22. Thesystem of claim 21, wherein the remote transmitter further comprises aCDMA modulator for CDMA modulating the information.
 23. The system ofclaim 12, further comprising an auxiliary program source fortransmitting at least one auxiliary information signal to at least oneremote location in a downlink direction along the cable only during atleast some of the blanking intervals of a cable channel.
 24. The systemof claim 12, further comprising an auxiliary program source fortransmitting at least one auxiliary information signal to at least oneremote location in a downlink direction along the cable, the programsource including circuitry for transmitting the at least one auxiliaryinformation signal onto at least part of the at least one video signalin a first polarity during one video frame of the at least one videosignal, and for transmitting the at least one auxiliary informationsignal onto a corresponding part of the at least one video signal in anopposite polarity during a next video frame of the at least one videosignal to produce visual cancellation of the auxiliary informationsignal, wherein the information is transmitted in a spectral regiondifferent from that including a chroma subcarrier of the at least onevideo signal.
 25. In a cable television system for transmitting at leastone video signal in a downlink direction over at least one cable, the atleast one cable having at least one amplifier along the at least onecable, a response module for communicating information from at least oneremote location along the at least one cable, the module comprising:amodulator for modulating the information from at least one remotelocation onto a first carrier; and a transmitter for transmitting themodulated information onto the at least one cable only during at leastsome of the blanking intervals of a first cable channel.